System and method for airflow sensing and monitoring

ABSTRACT

A system and method for measuring the airflow in an air handling unit, comprising a pressure plate with a plurality of apertures having a known surface area, a differential pressure manometer, and two. The first end of the leads is attached to a differential pressure manometer and second end of the leads is attached to the pressure plate. The pressure plate is placed in the filter rack of an air conditioning system the differential pressure manometer measures the differential pressure loss across the pressure plate allowing the user to determine airflow conditions and the location of obstructions. Additional embodiments of the system and method herein include placing two sensor tubes having apertures along the thereof at specific locations within the air handling unit that, when attached to a manometer, measure the differential pressure loss across the two locations. Various methods for establishing and monitoring proper airflow in an air handling unit are also contemplated.

PRIORITY INFORMATION

This application claims the benefit of U.S. Provisional Application No.61/230,916, filed Aug. 3, 2009, and U.S. Provisional Application No.61/354,807, filed Jun. 15, 2010.

TECHNICAL FIELD

The present invention relates generally to heating, ventilating and aircondition (“HVAC”) systems and more specifically to systems and methodsfor sensing, measuring, and monitoring airflow conditions within HVACsystems.

BACKGROUND OF THE INVENTION

Proper airflow is a critical component to assure maximum efficiency inforced-air ducted air conditioning (AC) systems. The Department ofEnergy sponsored Energy Star Survey determined that more than 50% ofair-conditioning installations have low airflow. Low airflow reducessystem efficiency (SEER), increases energy costs, results excessivemaintenance and repair costs, and leads to premature failure ofequipment.

Current methodology to measure and establish proper airflow isproblematic and unreliable. Methods known in the art, such as placing anair velocity meter inside an AC duct and then estimating thecross-sectional area of the duct, are far too complex and prone toinaccuracy for field technician charged with effectively diagnosingproblems with AC systems. More accurate and precise methods of measuringand establishing proper airflow typically require extensive techniciantraining, and expensive instrumentation and installation costs.

One example of a known method of measuring airflow in HVAC systemsincludes the use of “flow hoods.” A flow hood typically consists of alarge housing having a known area and an air velocity sensor placedtherein. The hood is then placed over an intake grill or return grill ofa given ducted AC system, and the air velocity is measured. The cleardownside to these flow hoods is that the large housing often renders theflow hood useless in buildings where the grills are too close to otherstructural elements and therefore the flow hood, while accurate, simplycannot be used.

Other examples of known methods for measuring HVAC airflow includetemperature-based methods. Typically, one first turns on the heatingelement within the system and then measures the temperature of the airgoing into the heater and the temperature of the air leaving the heater.Then, a series of calculations are carried out, resulting in adetermination of the airflow velocity. However, this indirect method ofcalculating airflow velocity can be very imprecise and inaccurate due tothe stratification of the temperature gradient across the system andtherefore is not effective in diagnosing problems within the HVACsystem, whether up-stream or down-stream from the air handling unit.

Known means for monitoring the performance and efficiency of an HVACsystem have severe limitations. Typical thermostats known in the art donot monitor the actual airflow conditions in its attendant HVAC system.Rather, they simply measure the temperature of the room to becooled/heated and provide a feedback-based switching system for the HVACsystem. While some of these thermostats have the ability to inform theuser whether a filter change is needed, this indication is usually basedsolely on the length of operation of the HVAC system between filterchanges and does not take into account the actual airflow conditionswithin the system.

Consequently, there is a marked need in the art for an easy-to-operate,cost-effective, integrated system and method for sensing, measuring, andmonitoring the airflow conditions within an HVAC system.

SUMMARY OF THE INVENTION

The present invention comprises several embodiments of a system andmethod for sensing, measuring, and monitoring the airflow in an HVACsystem, and more specifically, the air handling unit thereof. Oneembodiment comprises the use of a pressure plate having a known freearea which is placed in the filter rack of an air handling unit. Thepressure loss across the plate is measured using a manometer attached tothe plate by two leads, one on each side. The pressure loss is convertedto an airflow velocity measurement using known airflow data for theparticular air handling unit. Other embodiments comprise the use ofsensor tubes placed at specific locations within the air handling unitthat are attached to a manometer for determining the pressuredifferential across the two locations.

A comparison of the measured airflow velocity to the optimal airflowvelocity can be determined in order to assess whether there is anobstruction in the system. Further, the disclosed systems can be used tomonitor the actual performance of a given HVAC system over time and avisible or audible indicator can be employed to signal that a filterchange is needed or that there is an obstruction or other problem withinthe system, such as a dirty evaporator coil.

Accordingly, it is an object of the present invention to eliminate thehurdles of known methods for measuring and monitoring HVAC airflowconditions and allow an HVAC technician of average skill to accuratelyand precisely determine the airflow conditions and correct airflowdeficiencies for any HVAC system. It is a further objective of thepresent invention to provide the ability to monitor an HVAC systemduring its useful life to assure maximum energy efficiency andfiltration effectiveness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is side aspect view of one embodiment of the system of thepresent invention.

FIG. 2 is side cutaway view of one embodiment of the system of thepresent invention.

FIG. 3 is an exemplary chart determined in accordance with the method ofthe present invention, depicting the relationship between airflow anddifferential static pressure for a given air handling unit and pressureplate.

FIG. 4 is an exemplary graph employed in accordance with the method ofthe present invention, depicting the relationship between the percentageof air flow through a given air filter and the level of obstruction ofthe given air filter.

FIG. 5 is an exemplary chart employed in accordance with the method ofthe present invention, depicting various air filters with respect tocost and filter face velocity.

FIG. 6 is side view of another embodiment of the system of the presentinvention.

FIG. 7 is an expanded view of another embodiment of the system of thepresent invention, depicting sensor tubes mounted to an auxiliaryheater, wherein the sensor tubes are disposed between the auxiliaryheater and a blower (not shown).

DETAILED DESCRIPTION OF THE INVENTION

While the present invention will be described more fully hereinafterwith reference to the accompanying drawings, in which one or moreembodiments of the present invention are shown, it is to be understoodat the outset of the description which follows that persons of skill inthe appropriate arts may modify the invention herein described whilestill achieving the favorable results of this invention. Accordingly,the description which follows is to be understood as being a broad,teaching disclosure directed to persons of skill in the appropriatearts, and not as limiting upon the present invention.

Pressure Plate

FIG. 1 depicts one embodiment of the system of the present invention.Shown is air handling unit 10, supply duct 11, perforated pressure plate12 containing a plurality of apertures 13, and flexible leads 14 and 15.Air flows into the system in the direction of arrow 17. With referenceto FIG. 2, also shown is filter rack 18, blower 19, and heating element110. The dimensions of the pressure plate 12 correspond to thedimensions of the particular filter rack 18 of the air handling unit 10.In accordance with the method of the present invention, the combinedarea of the apertures 13 of the pressure plate 12 is calculated torepresent an air pressure loss equal to the known nominal airflowrating, measured in cubic feet per minute (cfm), of the particular airhandling unit 10 taking into account a standard low-pressure-loss airfilter under slightly used (dirty) conditions. Accordingly, the pressureplate 12 provides a stable surface across which to measure the pressureloss with predictability and repeatability.

In order to determine the optimal airflow for a given air handling unit10 in the field, an airflow/pressure loss relationship is firstcalculated under laboratory conditions. Accordingly, each specific airhandling unit 10 (or self contained air conditioning unit) model for anygiven manufacturer may be tested according to the method of the presentinvention:

The published nominal airflow for the subject air handling unit 10 isreviewed and noted. If the air handling unit 10 has provisions for amounted air filter, the filter is removed and a pressure plate 12 with aknown free area opening is inserted in the filter rack. The pressureplate 12 is designed to equally distribute the air across the face areaof the intake of air handling unit 10 in order to create sufficientpressure to provide repeatable differential static pressure readings atvarying airflow rates.

The differential static pressure across plate 12 is measured andrecorded using a differential pressure manometer 112 using two flexibleleads 14 and 15 which are attached to either side of the pressure plate12 and further to manometer 112. Next, pressure plate 12 is removed andthe nominal airflow is measured with a high accuracy flow meter, suchas, without limitation, a flow hood or air velocity meter known in theart. Additional differential static pressure measurements are thenperformed at varying airflow rates which are created either byrestricting the airflow at the inlet or outlet of the system and/orvarying the blower 19 speed of the air handling unit 10. Accordingly, byplotting the recorded data, an airflow/pressure loss table is generated,as shown by way of example in FIG. 3, for a particular air handling unit10. This plot depicts the relationship between the static differentialpressure and the actual airflow. Additional plots can be generated whichtake into account air-filters of varying size and filtration capability.

Pressure Plate—Establishing and Monitoring Proper Airflow

In order to establish and monitor proper airflow according to thepresent invention, one first determines the current airflow of aparticular air handling unit 10 in order to assess whether the airflowis sub-optimal, and secondly, determine the cause of the sub-optimalairflow and the location of the blockage (i.e. upstream or downstream).Accordingly, the airflow (without filter) for any specific air handlingunit 10 or air handling unit/filter combination can be determined bymeasuring the differential static pressure across the pressure plate 12and referring to the corresponding airflow/pressure loss plot (forexample, FIG. 3) for that specific air handling unit 10 or air handlingunit/filter-grille combination. This procedure allows the technician toaccurately determine the airflow with simple low cost devices where theuse of laboratory instruments is not practical.

Specifically, the airflow is determined by removing the filter from thefilter rack and inserting the appropriate pressure plate 12 thatcorresponds to the particular air handling unit 10. The technician thenmeasures the pressure loss across the plate 12 using a differentialpressure manometer 112 and determines the corresponding airflow by usingthe known airflow/pressure loss plot (for example, FIG. 3) for the airhandling unit 10. With reference to FIGS. 4 and 5, the technician canthen determine the optimal airflow, taking into account airflow loss dueto the type of air filter being used by referring to the airflow/filterdegradation relationship, which provides a reference for most standardfilter types and filter-rack size combinations.

Once the airflow has been assessed and adjustments and/or correctionshave been made to achieve the optimum airflow, the corresponding suctionpressure of the blower 19 (shown in FIGS. 1 and 2) may be measured andrecorded in real time at point 16. This establishes the reference pointof optimum airflow for the system regardless of variations caused bydirty filters, dirty coils, closed registers, and the like. A number ofvisible or audible devices may be used to monitor airflow and conditionsand signal deviation from the reference point. Such devices may be assimple as a visual indicator gage 111 or an audible alarm that may beincorporated into an electronic thermostat. The monitoring data may beused to calculate cost/benefit analysis for system efficiency andfiltration effectiveness by using the airflow/filter degradationrelationship shown in FIG. 4 and FIG. 5.

Sensor Tubes

FIG. 6 depicts an alternative embodiment of the system of the presentinvention. Shown is air handling unit 20, supply duct 21 with airflowing in the direction of arrow 27, auxiliary heater assembly 22, airvelocity pressure sensor tubes 24 and 25, heating/cooling coil 28,blower 29, motor 210, heating element 211, and differential pressuremanometer 212.

With reference to FIG. 7, in one embodiment, the sensor tubes 24 and 25are mounted directly in the auxiliary heater assembly 22, or on amounting plate (not shown) disposed within supply duct 21 when theelectric heater is not integrated into the air handling unit 20. Each ofsensor tubes 24 and 25 contain one or more apertures 23 locatedsubstantially toward the distal end of the tubes through which airejected from the blower 29 is sensed. In some embodiments, sensor tubes24 and 25 are stacked one upon the other such that the correspondingapertures 23 of the tubes are substantially co-incident.

As shown in FIG. 7, tube 25 is disposed between the blower 19 and tube24, with both sensor tubes 24 and 25 disposed between the blower 19 andheating element 211, such that tube 25 measures the total pressure andtube 24 measures the static pressure. The two sensor tubes 24 and 25 areattached to manometer 212, at their proximal ends. Air velocity pressureis determined by subtracting the static pressure from the totalpressure. Accordingly, with air flowing in the direction of arrow 213,the manometer 212 measures the air velocity pressure by sensing thedifference between the total pressure at sensor tube 25 and staticpressure at sensor tube 24.

With reference again to FIG. 6, in an alternative embodiment, sensortubes 24 and 25 may be located at the outlet 32 and inlet 31,respectively, of the blower 29. In this configuration, the manometer 212measures the pressure differential across the blower 29, which can beused to effectively determine obstructions or problems in the system,i.e. whether it is up-stream or down-stream of the blower. The advantageof this configuration is that there is typically a greater pressuredifferential across the blower than is typically found within theauxiliary heater assembly or, if omitted, within the supply duct 21.

As with the pressure plate embodiment, in order to determine the optimalairflow for a given air handling unit 20 in the field, anairflow/pressure loss relationship is first calculated under laboratoryconditions. Accordingly, each specific air handling unit 20 (or selfcontained air conditioning unit) model for any given manufacturer may betested according to the method of the present invention. The publishednominal airflow for the subject air handling unit 20 is reviewed andnoted. Sensor tubes 24 and 25 with a known free area opening (i.e.combined surface area of one or more apertures 23) are inserted betweenthe auxiliary heater 22 (if used) and blower 19. Alternatively, sensortubes 24 and 25 may be located at the outlet 32 and inlet 31,respectively, of the blower 29.

The differential static pressure between sensor tube 24 and sensor tube25 is measured and recorded using the aforementioned manometer 212.Next, sensor tube 24 and sensor tube 25 are removed and the nominalairflow is measured with a high accuracy flow meter. Additional airvelocity pressure measurements are then performed at varying airflowrates which are created by restricting the airflow inlet or outlet;and/or varying the fan speed of the blower 19 of the air handling unit20 (or self contained air conditioning unit). Accordingly, anairflow/air velocity pressure table is generated as shown by way ofexample in FIG. 3, for a particular air handling unit 20, and auxiliaryelectric heater (if used) combination. Additional plots can be generatedwhich take into account airflow losses from various air filter models ofvarious manufacturers.

Sensor Tubes—Establishing and Monitoring Proper Airflow

In order to establish and monitor proper airflow in an air conditioningsystem according to the second embodiment of the method of the presentinvention, one first determines the actual airflow to assess whether theairflow is sub-optimal, and make adjustments to fan speeds, dampers,duct sizing, etc. to attain optimal airflow. The sensor tube embodimentof the present invention allows the airflow to be measured for anysystem, regardless of airflow restrictions (air filters, size ofductwork, dampers, etc.) and for each specific air handling unit 20 thatis used in the system that has been laboratory tested with the presentinvention. This allows the technician to use simple low cost devices toquickly and accurately determine airflow if the use of laboratoryinstruments is not practical.

The technician measures the pressure loss across the sensor tubes 24 and25 manometer 212 and determines the corresponding airflow by using theknown airflow/pressure loss plot (for example, FIG. 3) for the airhandling unit 20. With reference to FIGS. 4 and 5, the technician canthen determine the optimal airflow, taking into account airflow loss dueto the type of air filter being used by referring to the airflow/filterdegradation relationship, which provides a reference for most standardfilter types and filter-rack size combinations.

In comparison to the pressure plate embodiment described herein, thesensor tube embodiments have additional benefits in that the sensor tubearrangement can be permanently installed for continuous monitoring andadjustment of the airflow. Accordingly, once the airflow has beenassessed and adjustments and/or corrections have been made to achievethe optimum airflow, the corresponding pressures may be measured andrecorded in real time with the use of manometer 212. If the optimalairflow falls below a given threshold value, a warning can be activatedwhich advises the operator of the AC unit to check the unit forobstructions or to change a dirty filter. In cases where the airflowdrop is drastic, a secondary warning can be delivered which instructsthe operator to contact a technician to service the unit or an automatedshutdown of the AC system may be initiated.

In the foregoing description, the present invention has been describedwith reference to specific exemplary embodiments thereof. However, itwill be apparent to those skilled in the art that a person understandingthis invention may conceive of changes or other embodiments orvariations, which utilize the principles of this invention withoutdeparting from the broader spirit and scope of the invention. Thespecification and drawings are, therefore, to be regarded in anillustrative rather than a restrictive sense.

1. A method for determining the airflow/pressure loss function in an airhandling unit, comprising: a. placing a pressure plate with a knownsurface area in the filter rack of said air handling unit whereby saidpressure plate is designed to equally distribute the air across the airintake of said air handling unit; b. measuring and recording thedifferential static pressure across said pressure plate using adifferential pressure manometer; c. removing said pressure plate andmeasuring the airflow of said air handling unit using a high accuracyflow meter; d. varying said airflow of said air condition system; e.repeating steps a-d; and f. determining the correlation between saiddifferential static pressure across said pressure plate and the actualairflow.
 2. The method in claim 1, further comprising varying saidairflow of said air handling unit by restricting said airflow at theinlet of said air handling unit.
 3. The method in claim 1, furthercomprising varying said airflow of said air handling unit by restrictingsaid airflow at the outlet of said air handling unit.
 4. The method inclaim 1, further comprising varying said airflow of said air handlingunit by increasing or decreasing the blower fan speed of said airhandling unit.
 5. A method for determining the airflow/pressure lossfunction for an air handling unit, comprising: a. placing a first end ofa first and second sensor tubes in said air handling unit wherein saidsensor tubes have one or more apertures of a known free area and whereina second end of said first sensor tube is attached to a first inlet of adifferential pressure manometer and the second end of said second sensortube is attached to a second inlet of said differential pressuremanometer; b. measuring and recording the differential static pressureacross said first and second sensor tubes using said differentialpressure manometer; c. removing said sensor tubes from said air handlingunit and measuring the airflow of said air handling unit using a highaccuracy flow meter; d. varying said airflow of said air handling unit;e. repeating steps a-d; and f. determining the correlation between, saiddifferential static pressure across said sensor tubes and the actualairflow.
 6. The method in claim 5, further comprising varying saidairflow of said air handling unit by restricting said airflow at theinlet of said air handling unit.
 7. The method in claim 5, furthercomprising varying said airflow of said air handling unit by restrictingsaid airflow at the outlet of said air handling unit.
 8. The method inclaim 5, further comprising varying said airflow of said air handlingunit by increasing or decreasing the blower fan speed of said airhandling unit.
 9. The method in claim 5, wherein said first end of saidfirst and second sensor tubes are disposed between a heating elementsand a blower of said air handling unit.
 10. The method of claim 9,wherein said second sensor tube is disposed between said first sensortube and said blower.
 11. The method of claim 9, wherein said one ormore apertures of said first and second sensor tubes are substantiallyco-incident.
 12. The method of claim 5, wherein the first end of saidfirst sensor tube is disposed at the outlet of a blower of said airhandling unit, and the first end of said second sensor tube is disposedat the inlet of a blower of said air handling unit.
 13. A system formeasuring the airflow in an air handling unit, comprising: a firstsensor tube having a one or more apertures; a second sensor tube havingone or more apertures; a differential pressure manometer; wherein afirst end of each of said sensor tubes is attached to said differentialpressure manometer and a second end of each of said sensor tubes isdisposed between a heating element and a blower of said air handlingunit; wherein said differential pressure manometer measures thedifferential pressure loss across said sensor tubes.
 14. The system ofclaim 13, wherein said sensor tubes are flexible and resilient.
 15. Thesystem of claim 13, wherein said second sensor tube is disposed betweensaid first sensor tube and said blower.
 16. The system of claim 15,wherein said one or more apertures of said first and second sensor tubesare substantially co-incident.
 17. A system for measuring the airflow inan air handling unit, comprising: a first sensor tube having a one ormore apertures; a second sensor tube having one or more apertures; adifferential pressure manometer; wherein the first ends of each of saidsensor tubes is attached to said differential pressure manometer, thesecond end of said first sensor tube is disposed at the outlet of ablower of said air handling unit, and the second end of said secondsensor tube is disposed at the inlet of a blower of said air handlingunit; wherein said differential pressure manometer measures thedifferential pressure loss across said sensor tubes.
 18. The system ofclaim 17, wherein said sensor tubes are flexible and resilient.
 19. Amethod for establishing and monitoring proper airflow in an air handlingunit comprising placing a first end of a first and second sensor tubesin said air handling unit wherein said sensor tubes have one or moreapertures of a known free area and wherein a second end of said firstsensor tube is attached to a first inlet of a differential pressuremanometer and the second end of said second sensor tube is attached to asecond inlet of said differential pressure manometer; measuring thedifferential static pressure across said sensor tubes using saiddifferential pressure manometer; calculating the present airflow acrosssaid sensor tubes by applying a known airflow/pressure loss function tosaid pressure loss; determining the optimal airflow of said air handlingunit, taking into account airflow loss due to the type of air filter tobe used by applying a known airflow/filter degradation relationship;correcting said present airflow in order to establish said properairflow; and monitoring said proper airflow for airflow deviations usinga visible or audible indicator.
 20. The method of claim 19, wherein saidleads are comprised of flexible tubing.
 21. The method of claim 19,wherein the first end of said first sensor tube is disposed at theoutlet of a blower of said air handling unit, and the first end of saidsecond sensor tube is disposed at the inlet of a blower of said airhandling unit.